Biochemical oxidation of carbonaceous and nitrogenous substrates, in aqueous waste streams, is typically mediated by microorganisms capable of catalyzing the oxidative processes under conditions ranging from strict aerobiosis to strict anaerobiosis. The selection of the specific process environment depends on the nature of the substrates, their concentration and treatment objectives. High strength wastewater is characterized by high substrate concentrations, as measured by the chemical oxygen demand (COD) or the five-day biochemical oxygen demand (BOD5), and high nitrogen content, as measured by ammonia-, nitrite- or nitrate-nitrogen. Conversion of BOD5 to carbon dioxide and water, and transformation of ammonia to nitrite and nitrate in a process termed nitrification, requires a supply of oxygen sufficiently high to satisfy the stoichiometric requirements of these processes.
Biological processing of high strength wastewater in terrestrial or space environments presents serious challenges, stemming mainly from mass transfer limitations of substrate and oxygen. Further, a major issue in space applications is the absence of gravity which introduces problems associated with separation between solid-liquid and liquid-gas phases.
Immobilized, cell packed bed bioreactors (ICPB) have been used extensively for the treatment of wastewater on earth and can provide solutions to problems associated with microgravity. Conceptual models of advanced life support (ALS) integrated systems design mandate approximately 100% closure with respect to the water loop Drysdale A. E., et al., xe2x80x9cA More Completely Defined CELSSxe2x80x9d, SAE Paper 941292, 24th International Conference on Environmental Systems and 5th European Symposium on Space Environmental Control System, Friedrichshafen, Germany, Jun. 20-23, 1994.). Water reclamation from various aqueous streams and reuse is thus imperative. Water rich liquid streams in space/space vehicle habitats include washwater, utility water (food preparation, laundry), urine and condensate water. Mixtures of the first two streams (washwater, utility water) are commonly termed greywater. Estimated quantities of urine and greywater vary in the range of between 1.3-2.1 liters of urine waste and 20-30 liters of greywater waste per person per day. (Wieland P. O., xe2x80x9cDesigning for Human Presence in Space: An Introduction to Environmental Control and Life Support Systemsxe2x80x9d, NASA Reference Publication 1324, 1994.; Wydeven T. and Golub M. A., xe2x80x9cGeneration Rates and Chemical Composition of Waste Streams in a Typical Crewed Space Habitatxe2x80x9d, NASA Technical Memorandum 102799, Ames Research Center, 1990). With the exception of condensate water which is low in organic content, the other liquid streams contain varying amounts of organic loads and require treatment prior to any possible reuse. Various reuse scenarios include utilization of the reclaimed water as hydroponic solution water, utility water, or potable water. Evidently, each of these reuse scenarios dictates and sets the desired treatment objectives. These objectives include, but are not limited to: organic carbon removal, nutrient reclamation and reuse in hydroponic solutions, and water reclamation. Essentially the first two objectives can be summarized as carbon oxidation and nitrification. Research conducted over the last ten years has shown that biological processes for treatment of urine, condensate, and grey water combined streams have a demonstrated potential for use as a primary water processor (Petrie G. E., et al., xe2x80x9cDevelopment of Immobilized Cell Bioreactor Technology for Water Reclamation in a Regenerative Life Support Systemxe2x80x9d, SAE Paper 911503, 21st International Conference on Environmental Systems, San Francisco, Jul. 15-18, 1991; Petrie G. E., et al., xe2x80x9cImmobilized Cell Bioreactors for Water Reclamation: Process Stability and Effect of Reactor Designxe2x80x9d, SAE Paper 921227, 22nd International Conference on Environmental Systems, Seattle, Jul. 13-16, 1992.) or a trace polisher in an integrated bioregenerative life support water recovery system (Miller G. P. et al., xe2x80x9cFurther Applications of the Use of Biological Reactors to Remove Trace Hydrocarbon Contaminants from Recycled Waterxe2x80x9d, SAE Paper 921273, 22nd International Conference on Environmental Systems, Seattle, Jul. 13-16, 1992; Miller G. P. et al., xe2x80x9cUsing Biological Reactors to Remove Trace Hydrocarbon Contaminants from Recycled Waterxe2x80x9d, SAE Paper 911504, 21st International Conference on Environmental Systems, San Francisco, Jul. 15-18, 1991). Because of the well established performance reliability, small energy and volumetric requirements, various configurations of immobilized cell bioreactors have been preferred over their suspended growth counterparts. Collaborative work performed by NASA and aerospace contractors has focused on immobilized cell bioreactors operating as plastic media packed beds. Two-stage packed bed bioreactors containing porous and non-porous plastic media accomplishing carbon oxidation in the first stage and nitrification in the second were initially studied (Verostko C. E., et al., xe2x80x9cA Hybrid Regenerative Water Recovery System for Lunar/Mars Life Support Applicationsxe2x80x9d, SAE Paper 921276, , 22nd International Conference on Environmental Systems, Seattle, Jul. 13-16, 1992). The performance of these reactors with respect to both chemical oxygen demand (COD), and urea degradation at hydraulic retention times (HRT) in the range of 24-48 hr was satisfactory (greater than 97% and 99%, respectively) but decreased significantly for HRTs in the range of 12-24 hr (65% and 91%, respectively) (Petrie G. E., et al., xe2x80x9cImmobilized Cell Bioreactors for Water Reclamation: Process Stability and Effect of Reactor Designxe2x80x9d, SAE Paper 921227, 22nd International Conference on Environmental Systems, Seattle, Jul. 13-16, 1992). An immobilized cell bioreactor (ICB) essentially consisting of a foam covered plate reactor was also studied in parallel. The parallel plate reactor performance was over 95% and 99% total organic carbon (TOC) and urea reduction for all HRTs in the range of 12-24 hours. Full-scale experiments for both bioreactor types verified previous findings (Nacheff-Benedict M. S. et al., xe2x80x9cAn Integrated Approach to Bioreactor Technology Development for Regenerative Life Support Primary Water Processorxe2x80x9d, SAE Paper 941397, 24th International Conference on Environmental Systems and 5th European Symposium on Space Environmental Control System, Friedrichshafen, Germany, Jun. 20-23, 1994).
Immobilized cell bioreactors with packed or fluidized bed, provide a unique environment for microbial growth resulting in high biomass concentrations. Packing materials commonly used include ceramic saddles, stainless steel wire spheres, polypropylene toroids, reticulated polyester foams, matted reticulated polypropylene sheets, polypropylene strands and sand. The main features of immobilized cell bioreactors are the support media for microbial attachment with larger surface area which are better for conversion efficiency; the absence of a microbial wash-out flow-rate, and the elimination of the need for concentrated biomass recycle from a clarifier. The advantages of these reactor configurations over conventional, completely stirred tank reactors (CSTR) systems for organic removal and nitrification/denitrification are well established. Biomass concentrations as high as 5-40 g/L of reactor volume have been reported when using solid support particles (Cooper, R. F. and B. Atkinson. Editors of: Biological Fluidized Bed Treatment of Water and Wastewater. Ellis Horwood Limited Publishers, 1981). High biomass concentrations greatly enhance process efficiency resulting in substantial reductions in treatment time and reactor volume. ICBPs can operate both in aerobic and oxygen limiting modes. A major problem with the operation of such aerobic reactors is oxygen distribution and gaseous by-product formation. Phase separation in packed beds under microgravity conditions, has been a major problem.
Greywater generated in closed environments such as a space station, a space vehicle or a submarine contains high concentrations of biodegradable carbon compounds and nitrogen in the form of various amino acids and urea. Liquid wastes generated from various farming activities also have high levels of carbon and nitrogen and are difficult to treat by conventional aerobic processes. For instance, liquid swine wastes are characterized by high BOD5 and COD strengths. This high strength wastewater exerts a high oxygen demand on the treatment system if complete conversion to innocuous products is to be realized. Typical concentrations of carbon and nitrogen in greywater are in excess of 800 mg/L BODS, and 500 mg/L of ammonia-nitrogen(NH3-N), respectively. These concentrations are substantially higher than the corresponding BOD5 and ammonia concentrations observed in municipal wastewater. Conventional attached growth systems such as trickling filters and packed bed bioreactors, operating at atmospheric conditions, cannot effectively cope with the mass transfer demands, in terms of substrate and oxygen, that are required for efficient treatment of high strength wastewater. In addition, these systems operate in a three phase mode meaning that the solid, liquid and gaseous phases coexist in the packed bed bioreactor unit, which makes phase contact and separation impossible under microgravity conditions. Most biological processes currently in operation require a solid-liquid separator after the bioreactor, in order to separate the biomass from the treated effluent prior to discharge.
U.S. Pat. Nos. 5,403,487, 5,463,176, 5,543,039, 5,686,304, and 6,132,602 describe various approaches which enhance oxygen transfer and process performance in attached growth packed bed bioreactors. U.S. Pat. No. 5,543,143 describes generation of microbubbles for enhanced oxygen transfer. U.S. Pat. No. 5,997,736 describes nitrogen conversion by specific microorganisms. U.S. Pat. No 4,192,742 describes a system wherein wastewater is passed through a pressurization tank and a gas tight biological filter bed. The liquid in the first tank comes into direct contact with an oxygen-containing gaseous phase above it. The oxygenated wastewater is then introduced to the biological filter, which also operates under pressure, and is subsequently discharged to the environment. Both the oxygenation tank and the biological filter operate with a gaseous headspace, thus forming a two-phase system, which makes them unsuitable for microgravity operation. Moreover, the single-pass of the wastewater through the biological filter limits the performance of the system for the treatment of high strength streams. Another limitation of this system is that oxygen exchange occurs through the interface of the liquid and gas phases which is fixed by the dimension of the chamber.
Another method widely used in the biological treatment of wastewater by attached growth bioreactors, is the recycling of a portion of the effluent to a point upstream of the oxygenation device. This approach also enhances oxygen transfer and improves the overall performance of the system, but becomes uneconomical for the treatment of large volumes of wastewater when the operation is carried out using air at atmospheric pressure. Further, this approach suffers from similar limitations to pressurized two-phase systems during treatment of high strength streams and in the absence of gravity.
Therefore, there is a need for an improved biological method and apparatus for treatment of high strength wastewater in terrestrial and microgravity environments.
An object of the present invention is to provide an apparatus for wastewater treatment comprising at least one immobilized cell packed bed bioreactor, and at least one membrane oxygenation module attached to an external recirculation line.
Another object of the present invention is to provide a system for treating wastewater comprising at least one immobilized cell packed bed bioreactor, and at least one membrane oxygenation module attached to an external recirculation line.
A further object of the present invention is to provide a method of treating wastewater containing organic carbon and ammonia using the apparatus of the present invention by removing organic carbon and nitrifying high strength wastewater.